An unprecedented voyage is underway to find ways to protect the Great Barrier Reef.

Two summers of high water temperature have proven toxic for the reef, causing mass coral bleaching.

A group called Great Barrier Reef Legacy has gathered teams of researchers and reef experts from Australia and around the world, and are conducting the biggest underwater mapping and sampling expedition since the bleaching occurred.

They are also searching for so-called "super corals" that survived the bleaching.

The director of GBR Legacy and veteran tour operator John Rumney said the time had come to do something about the death of coral across large parts of the reef.

"I've been out here for 40 years and observed the changes in the reef," he said.

"When I first got here it was absolutely mind-blowingly beautiful and diverse, and over time we've seen it decline.

"We really need to start taking care of this, we're beyond the point of it taking care of itself."